The invention relates to the field of semiconductor wafer processing, and in particular to utilization of a mass spectrometer or similar sensor in conjunction with manufacturing or processing apparatus for detection of aberrant conditions, such as the presence of certain contaminants on a semiconductor substrate.
Many manufacturing processes which occur in a vacuum or other controlled atmosphere are sensitive to levels of one or more contaminants, process by-products, or other substances present in a process chamber(s).
In the field of semiconductor substrate manufacturing, PVD (Physical Vapor Deposition) metallization cluster tools require a complex vacuum system to ensure low partial pressures of water, oxygen, nitrogen and hydrocarbons. These compounds act as contaminants which degrade the quality of different metal films deposited by sputtering. Therefore, the presence of these compounds must be continuously monitored to safeguard process quality.
Residual photoresist present on a semiconductor (e.g., silicon) wafer which is about to undergo sputter deposition of metal (e.g., aluminum) interconnects is a typical example of such an undesirable contaminant in a semiconductor manufacturing process. If the photoresist-contaminated wafer reaches the sputter module, and the deposition process is initiated, then the sputter module will be severely contaminated by the photoresist. The wafer being processed will be irreparably damaged, and the sputter module will have to be cleaned before further wafers can be processed. The process of cleaning a sputter module is both time consuming and expensive.
Current semiconductor sputtering tools generally employ a separate process chamber wherein the wafer, after it is inserted into the overall manufacturing tool, can be degassed before further processing. In this chamber, the wafer is rapidly heated to drive off normally adsorbed contaminants such as water vapor. The degas module removes water by heating the wafer either with tungsten/halogen lamps while under vacuum, or by placing the wafer on a heated chuck while argon flows on the back side of the wafer. If the wafer is also contaminated with residual photoresist, gases characteristic of the specific type of photoresist present will be desorbed from the wafer. When small amounts of photoresist remain on the wafer, the above degas step will cause pyrolysis of the photoresist which breaks the large polymer molecules into several certain gaseous compounds.
It is known that the presence of gases can be determined in a sampled gas environment using a mass spectrometer, such as those manufactured and sold by Leybold Inficon, Inc. of East Syracuse, N.Y. The presence of gases is determined by use of partial pressures of the environment and the gas(es) in question. Using a mass spectrometer, it is possible to monitor the levels of these characteristic gases by measuring the signal intensities of the appropriate mass-to-charge ratios of ions produced by these substances. If the signals at these masses exceed some predetermined upper limit during the degas process, it can be concluded that excessive amounts of photoresist are present.
Though ordinarily, it would seem likely to perform such a measurement, it is also known that modem semiconductor processing tools have been developed which allow simultaneous processes to be occurring in various chambers connected to the tool. Therefore, and when a wafer is transferred from one of these other modules (chambers) to the wafer handling chamber to which the degas module is attached, a pressure burst may occur in the degas module. This pressure burst can cause erroneously high levels of the masses being monitored by the mass spectrometer. It has been determined, however, that the duration of the signals produced by pressure bursts extend over a period of time which is significantly shorter than that of the degas process itself.
There is a need to provide a detector which is able to measure with certainty the small amounts of compounds which are produced when residual photoresist undergoes pyrolysis at the degas module, in order for the process to be halted, so as to prevent further contamination of PVD modules, and the extensive downtime required to clean the modules.
It is an object of the present invention to improve the state of the art of semiconductor manufacturing processes.
It is a further object of the present invention to detect the presence of impurities on a semiconductor wafer prior to high level vacuum processing so as to prevent downtime of a manufacturing tool.
It is yet a further object of the present invention to integrate the detection of impurities into the processing protocol either to allow automatic shutdown of the tool, or at a minimum, to notify the operator of a contamination condition.
Therefore and according to a preferred aspect of the present invention, there is provided a processing apparatus for determining the presence of aberrant conditions in a manufacturing process, said apparatus comprising:
a manufacturing tool having an interior within which said manufacturing process is performed and control means for controlling said manufacturing process; and
a sensor in communication with the interior of said manufacturing tool, said sensor having means for determining mass constituents of at least one sampled gas created during said manufacturing process and producing signals indicative of the intensities of said constituents, said sensor further including means for detecting when signals produced by said sensor has exceeded a predetermined value.
Preferably, the detecting means includes a timing circuit which allows the sensor, preferably a mass spectrometer, to distinguish the presence of signals which are characteristic of transient processing characteristics in comparison to longer signals that are representative of an acute processing problem, such as the presence of certain impurities. According to a preferred technique, an algebraic Boolean expression, using AND and OR logic, can be created to initiate the timing circuit only if certain binary conditions (e.g., meeting a predetermined ion current limit) are met.
Using similar logic, other processing conditions having output variables capable of being converted into binary values can also be monitored. The presence of such conditions, as evaluated through the above Boolean logic, can produce a signal which can be directly input to the manufacturing tool to terminate the process automatically or at a minimum to alert an operator thereof.
According to another preferred aspect of the invention, there is provided a processing apparatus for determining the presence of nontransient conditions in a semiconductor substrate manufacturing process, said apparatus comprising:
a manufacturing tool having an interior including a plurality of chambers within which said semiconductor substrate manufacturing process is performed and control means for controlling said manufacturing process; and
at least one sensor in communication with the interior of said manufacturing tool, said sensor being a mass spectrometer having means for determining mass constituents of at least one sampled gas created during said manufacturing process and producing representative signals indicative thereof, said sensor further including means for detecting signals produced by said sensor which have exceeded a predetermined value including a timer which is activated only upon detection of signals exceeding the predetermined value.
Preferably, the timer includes means for sending an output signal to said manufacturing tool if said timer exceeds a predetermined duration and is connected to said control means to cause termination of the manufacturing process automatically.
The sensor is preferably a mass spectrometer having means for producing and detecting ions having specified mass to charge ratios, said detecting means being capable of detecting representative signals of said specified ions, said sensor further including a plurality of relays, each relay having at least one setpoint which is triggered when at least one specified ion signal has exceeded a predetermined intensity.
According to the invention, the triggering of setpoints of certain preselected relays produces an output signal which is transmitted to said timing circuit for activating said timer. The time duration of said timer is selected to be greater than the known time duration of transient processing effects produced within the manufacturing tool such that the output signal generated by said timing circuit effectively screens the transient processing effects.
According to yet another preferred aspect of the invention, there is provided a method for determining the presence of nontransient processing conditions in a manufacturing process, said method including the steps of:
sampling specified mass constituents of at least one gas present within the interior of a manufacturing tool used in said manufacturing process;
activating a timer only if predetermined levels of certain mass constituents of said at least one gas are exceeded, said timer being set to a predetermined time interval which is greater than known durations exhibited by transient processing conditions; and
outputting a signal if said timer exceeds the predetermined time interval.
The method preferably includes the step of automatically terminating the manufacturing process if the timer exceeds the predetermined time interval or at a minimum to alert a process operator if the timer generates said output signal.
The sensor capable of performing the sampling, (e.g. a mass spectrometer) preferably has a set of relays which are part of the timing circuit or alternately the sensor includes relay logic including a plurality of setpoints which can be separately triggered when at least one signal exceeds a preselected value, said method including the steps of:
identifying materials present in anomalous processing conditions; and
preselecting the setpoints of said sensor in accordance with maximum levels of mass constituents corresponding to the identified materials.
Most preferably, the above timing step is initiated only upon the triggering of a predetermined combination of said setpoints. The above method has been demonstrated to be particularly effective in identifying the presence of photoresist in a vacuum deposition process.
An advantage of the present invention is that the inclusion of a timer circuit in combination with a sensor as described above allows the presence of normal processing steps, such as pressure bursts, to be discriminated against longer duration signals which are more likely to be indicative of contamination or other long-term conditions.
A further advantage is that the manufacturing tool is configured to receive input from the above circuit directly and to alert the operator of the processing apparatus if a predetermined condition is met.
These and other objects, features, and advantages will be readily apparent from the following Detailed Description which should be read in accordance with the accompanying drawings.